1. Field of the Invention
This invention relates to apparatus for flanging sheet metal blanks comprising a holding-down mechanism, which is adapted to hold down a sheet metal blank on a backing structure and comprises a holding-down shoe that is composed of a plurality of segments arranged in a row that is parallel to a bend line about which the blank is to be flanged. Said segments comprise mid-segment means and displaceable segments which are disposed on opposite sides of said mid-segment means and are slidably mounted on a track that is rigid with a holding-down ram and extends parallel to said bend line. Said displaceable segments are displaceable by means of two adjusting rods, which extend in the direction of said bend line on opposite sides of said mid-segment means.
2. Description of the Prior Art
From EP-A-0 105 091 it is known that the length of a holding-down shoe can be adapted to the length of the flange-forming portion of a sheet metal blank if the holding-down shoe comprises a plurality of displaceable segments, which are slidably mounted on a track which is parallel to the bend line about which the blank is to be flanged. The length of the shoe can be adapted in relatively coarse steps to the size of the blank in that a suitable number of displaceable segments are used in the shoe and those segments at the ends of the shoe which are not required are displaced out of the range of the blank to be flanged. To permit a fine adjustment, the shoe comprises a set of narrow mid-segments, which are pivotally movable for selective insertion into the row of active segments. In such an arrangement the length of each of the narrow mid-segments along the bend line will determine the increment in which the length of the shoe can be adapted to the length of the workpiece.
The movement of the displaceable segments to the mid-segments and the displacement of the end segments out of the range of the blank are performed by two adjusting mechanisms, which are disposed on each side of the mid-segments. One of said two adjusting mechanisms comprises an adjusting rod, which extends in the direction of the bend line and is connected by a tension-resisting joint to one of the displaceable segments which are nearest to the mid-segments. The other of said adjusting mechanisms comprises a one-way coupling finger and a screw drive, which extends parallel to said bend line and is operable to adjust said coupling finger. The latter can selectively be inserted between two adjacent displaceable segments to divide the segments on that side of the mid-segments into two parts, one of which can be displaced by an operation of the screw drive. By means of that combination of two adjusting mechanisms the segments can be adjusted to adapt the length of the shoe to the size of the workpiece. But the mechanisms for adjusting the segments represent an expensive and bulky structure and involve the disadvantage that considerable non-productive times are required for the idle movement of the coupling finger along the bend line to the position at which said finger is to be inserted.
In order to avoid said non-productive times for the idle adjustment of the coupling finger, it has been proposed in EP A-0 186 909 to provide a flanging apparatus in which those intermediate displaceable segments which are disposed between each terminal displaceable segment and a mid-segment are mounted on a shaft which is parallel to the bend line and said intermediate segments can be non-rotatably connected to said shaft by a releasable key. In that case the shaft can be rotated to impart to selected intermediate displaceable segments a pivotal movement so as to insert them as required into the row of active segments of the holding-down shoe. Those intermediate displaceable segments which are not required at a time remain in an inoperative position because they are not locked to the shaft by the associated releasable key. In such an arrangement the length of the holding-down shoe is adapted to the length of the flange-forming portion of the blank in that selected intermediate displaceable segments are pivotally inserted into the row of segments and the terminal segments are then displaced into engagement with the inserted intermediate displaceable segments. For that purpose the two terminal segments of the holding-down shoe are operatively connected to a screw drive having a screw formed with oppositely handed screw threads so that the two terminal segments can be displaced equal distances in mutually opposite directions. In addition to the length adjustment in coarse steps by the insertion of selected intermediate displaceable segments, a fine adaptation can be effected by means of a set of narrow segment plates, which can be pivotally moved from an inoperative outer position to an operative position in which they are disposed between adjacent mid-segments. To permit such an insertion the mid-segments and those intermediate displaceable segments which adjoin the mid-segments must be displaced along the bend line. For this purpose the mid-segments are axially coupled to the shaft means on which the intermediate displaceable segments are mounted so that the mid-segments can be axially adjusted in unison with those shaft means, which consist of two shaft sections, which can axially be displaced in mutually opposite directions. That arrangement also involves relatively expensive means for adjusting the various segments.